Monday, March 28, 2011

Like the Golden Gate Bridge...

The new tube motor is in place and gets its open & close stop limits set, and final wiring is completed.

Our attention turns to the tube motor controlling the north ridge vents. It hasn't been operating automatically as it normally has. It still opens and closes when the switch is operated manually, albeit, when the switch is put to the open position, the skylight closes, and when the switch is put in the close position, the skylight opens, but hey, heretofore it has been doing so automatically; closing when temperature inside is being conserved, and opening when temperature inside is being vented. But lately it stopped behaving and now just sits there oblivious to its environment.

My technician helper noticed that the close stop limit looked a little too close for comfort, so we decided to adjust the motor's stop limits since we were right there with the control box and limit adjusting tool. With the control box we can open and close the skylight vents as we stand right there on our ladders at the ready to adjust the motors limit settings. Throwing a 3 position toggle switch on the control box alternately opens, stops and closes the bank of vents, allowing us to fine tune the stop limit settings while we observe the position of the vents.

First, we opened the vents slightly to then test the close stop limit. Toggling to the "close" position, we watched and listened as the vents closed. A subtle ca-thunk sound beyond just 'closed' told us that indeed the motor was pulling the vents closed too much. He toggled the switch the other way to open the vents a few inches and then turned the adjustment setting on the motor housing to make the close stop limit activate sooner.

Unbeknownst to us, the 'subtle ca-thunk' involved two brass screws attaching a distant rack bracket to a skylight vent wooden sash to snap off, and the rack fell back away from the sash, rotating on the steel shaft to an inverted position. (Follow the link to an archived post detailing what the rack and pinion system looks like) When Ben toggled the switch to 'close' again, the pinion gear drove the inverted shaft upward where it caught an edge of the wooden roof frame and drove the steel shaft away from its mooring in the pillow block screwed to a rafter, ripping the screws out of the bottom of the rafter and splitting the rafter to boot in the process.

I suppose it's just as well it happened when we were there to stop things when we heard the horrendous snap. Had it happened automatically, either the steel shaft would have been bent beyond repair, or other unimaginable damage to the skylights or roof frame could have occurred.

Fortunately, after disengaging the rack from the pinion gear and its wedged position against the roof frame, the steel shaft appeared unbent. The rafter was repaired with stainless steel screws and gorilla glue, and the rack bracket was resecured to the vent sash. It was necessary to move it slightly to one side, because the old broken off screws still remain in their original holes, making it impossible to reattach the bracket in the same place.

Next blog post takes a look at resetting the stop limits.

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